It’s so tiny it’s almost invisible. You probably haven’t even noticed its existence. But if you do have one of these tiny holes beside your ear, you’re very lucky: only 1% of the population has one.

It’s called the preauricular sinus, or preauricular dimple, and it’s located at the point where the ear cartilage joins the face.

If you’ve just dashed to the mirror, or turned around to check your colleagues’ ears for these dimples (yes, we did too), then don’t worry: these curious little holes are mostly harmless.

It’s just a rare birth defect – a congenital malformation of the preauricular tissues that occurs around week six of gestation. Preauricular sinus was documented for the first time in 1864 by Van Heusinger. The theory is that they’re an evolutionary remnant of fish gills.

Approximately 50% of these holes appear on the right side of the head only.

If you happen to have one on both sides, then take a look at your parents’ ears: the chances are it’s hereditary.

And now, the bad news.

Usually, this tiny hole poses no health risks at all. But – prepare yourself – if the hole gets infected or forms a cyst, it will need to be treated. If you’re feeling particularly adventurous today (or if you’re just in the mood to be grossed-out) google “preauricular sinuses”. You’re welcome.

However, even if the hole does get infected, it’s not life threatening, and can be treated with antibiotics or, failing that, a minor operation.

Globally, it’s estimated that between 0.1% and 0.9% of Europeans and Americans have preauricular sinuses. These figures are higher in other places: the tiny holes can be found in the ears of 2.5% of Taiwanese and 10% of Africans.